Information of the economic impact and costs of AIDS is of critical importance in planning programs, allocating resources, and projecting costs. In order to track the utilization and costs of persons with AIDS on an ongoing basis, policy makers, researchers and planners will need a cost-effective source of information . Information reported to date on the costs of treating persons with AIDS has come from two sources: special studies, usually involving medical record review, and routinely collected hospital discharge data bases maintained by private firms and federal and state agencies. Information from special studies has several advantages but it is limited as a national source of information because it is relatively expensive to collect, local in scope, and not generalizable because it is limited to the patients treated in a few participating institutions. Routinely collected data may be a cost- effective source of information on AIDS for ongoing health services research and surveillance purposes. however, the accuracy and completeness of such information for studying utilization and costs of patients with AIDS is as yet not known. The Boston University School of Public Health and the AIDS Surveillance Program of the Boston Department of Health and hospitals propose to collaborate on a project to accomplish three purposes. First we will investigate the feasibility of using routinely collected Uniform Hospital Discharge Data Set (UHDDS) information to track cross-validating the Surveillance Program Registry data to determine the extent to with persons with diagnostic codes indicating AIDS do have AIDS. Second, we will use the results of the validation process to identify and types of patients missing from the AIDS Surveillance Registry to assist the Program staff in improving their case finding procedures. Third, we will use the data base developed through the validation process to demonstrate the use of the UHDDS data to describe the hospital use and charges of patients with AIDS, including the characteristics of patients, the hospitals providing treating, and the hospital stays. we will assess the performance of the newly developed HIV-related Diagnosis Related Groups (DRGs) in identifying patients with AIDS and in describing their resource use (as proxied by length of stay and charges).